1. Field of the Invention
The present invention relates to a semiconductor light emitting device using nitride semiconductor (InXAlYGa1-X-YN, 0≦X, 0≦Y, X+Y≦1) and a method of manufacturing the same.
2. Description of the Background Art
Nitride semiconductor receives attentions as a variety of semiconductor devices such as light emitting devices, and for example, blue LED (Light Emitting Diode), blue-green LED, and the like have been put to practical use.
Conventionally, nitride semiconductor light emitting devices are manufactured by growing nitride semiconductor in a stacked manner on an insulative substrate such as sapphire, spinel, lithium niobate, or neodymium gallate. However, when sapphire is used as a substrate material, (i) opposite electrodes have to be taken out from the same surface side of the sapphire substrate since sapphire is insulative, in other words, electrodes cannot be taken out from the top and the bottom of the substrate, (ii) accordingly, the chip size is increased so that a large number of chips cannot be obtained from a wafer, and (iii) because of high hardness and lack of cleavability of sapphire, sophisticated technique is required to form chips.
On the other hand, an attempt has been made to grow nitride semiconductor on a conductive substrate such as silicon carbide, silicon, zinc oxide, gallium arsenide, or gallium phosphide, which is, however, very difficult in the present situations.
In order to solve such problems, for example, Japanese Patent Laying-Open No. 2000-277804 discloses a method of manufacturing a nitride semiconductor light emitting device which ultimately has a conductive substrate, although a nitride semiconductor layer is grown in a stacked manner on an insulative substrate such as sapphire, and in which electrodes are taken out from the top and the bottom of the conductive substrate. With reference to FIG. 15, an exemplary method of manufacturing a nitride semiconductor light emitting device as disclosed in Japanese Patent Laying-Open No. 2000-277804 is schematically described.
First, a first ohmic electrode 1502 is formed on the almost entire surface of a nitride semiconductor layer 1501 stacked on a sapphire substrate. Here, nitride semiconductor layer 1501 at least includes, in order from the sapphire substrate, an n-type layer 1503 made of AlxGa1-XN (0≦X≦1) doped with a donor impurity, an active layer 1504 made of InYGa1-YN (0<Y<1), and a p-type layer 1505 made of AlXGa1-XN (0≦X≦1) doped with an acceptor impurity. Furthermore, a thin film, for example, of gold (Au), indium, tin, solder, or sliver paste is formed on the ohmic electrode 1502 in order to improve adhesiveness.
On the other hand, a second ohmic electrode 1507 is formed on the surface of a p-type GaAs substrate 1506 as a conductive substrate, and a thin film, for example, of gold (Au), indium, tin, solder, or silver paste is additionally formed thereon in order to improve adhesiveness. Next, the above-noted first ohmic electrode 1502 and the above-noted second ohmic electrode 1507 are affixed to each other and are compression bonded by heating. Next, the sapphire substrate is removed by polishing to expose n-type layer 1503 of nitride semiconductor layer 1501, and a negative electrode 1508 is thereafter formed on n-type layer 1503. On the other hand, a positive electrode 1509 is formed on the surface of p-type GaAs substrate 1506. A nitride semiconductor light emitting device (wafer) is thus obtained. Finally, the wafer having the positive electrode and the negative electrode is divided into a light emitting chip, for example, of 200 μm square, using cleavability of p-type GaAs substrate 1506, resulting in a nitride semiconductor light emitting chip having a structure as in FIG. 15.
Using such a manufacturing method, such a nitride semiconductor light emitting device can be realized that has a conductive substrate and has electrodes taken out from the top and the bottom of the conductive substrate.